1. Field of the Invention
This invention relates to a new and improved knitted fabric having improved electrical charge dissipation properties. More specifically, this invention relates to a readily manufactured knitted fabric comprised of nonconductive yarn that extends along the wale and combined with conductive fibers that form overlaps and underlaps within the nonconductive knit to such an extent so as to form a combined stitch construction, e.g., a modified "Queen's Cord" construction, providing an electrically conductive matrix capable of quickly dissipating charge along any direction of both the course and wale.
2. Description of the Prior Art
Electrostatic charge accumulates on clothing as the wearer moves his or her arms and legs and as he or she walks on non-conductive floor surfaces. The accumulation of such static charge poses a special problem in tight-fitting garments such as hosiery and sporting apparel in which static charge causes adjacent garments to cling to one another. This static cling causes both discomfort for the wearer and unpleasant shocks. Such charge accumulation can also create significant problems where the wearer works in an environment in which any static charge is undesirable or dangerous.
A need exists, therefore, for a means to control electrostatic charge accumulation on fabric, particularly fabric used in clothing worn by individuals who occupy or handle materials in areas in which an electrostatic discharge could be hazardous to the individual or could damage material which is being handled by the wearer, e.g., in operating rooms where potentially explosive gases are present or in "clean rooms" where electrically sensitive microcircuits are manufactured.
The utilization of fibers possessing electrical conductivity (e.g., metal fibers, fibers coated with electrically conductive material, or metal laminate filaments) in combination with common natural and manmade fibers to produce a woven, knitted, netted, tufted, or otherwise fabricated structure, which readily dissipates static charge as it is generated is well known.
In U.S. Pat. No. 3,823,035, issued to Sanders, an electrically-conductive textile fiber is disclosed in which finely-divided electrically conductive particles are uniformly suffused in a filamentary polymer substrate. Sanders discloses the interweaving of such electrically conductive fibers with ordinary threads made from natural fibers such as cotton or wool in an amount sufficient to render the electrical resistance of the fabric to a value of 10.sup.9 ohms/cm.
U.S. Pat. No. 4,312,913, issued to Rheaume, discloses a heat-conductive woven fabric comprising a plurality of fill layers of weavable yarns, each yarn comprising a plurality of fibers that are metallic or are coated with an effective amount of a metallic, heat conducting material. An angle weave pattern is woven through the layers of fill yarns in Rheaume, and this angle woven pattern extends from the top to the bottom of several layers of fill yarns.
Similarly, U.S. Pat. No. 4,296,855, issued to Blalock, also discloses a woven pattern of filler and warp yarns comprised of an electrically insulating material suffused with electrically conducting carbon particles, the warp and filler being woven in an open mesh configuration.
U.S. Pat. No. 4,422,483, issued to Zins, discloses a multiplicity of elongated filaments which are essentially parallel to each other and which form a single ply of a conductive thread for woven fabrics. The elongated filaments in Zins are non-textured continuous, non-conductive filaments or warp threads which are combined together with conductive filaments or fill threads to form a conductive woven fabric.
Neither Sanders, Rheaume, Blalock or Zins disclose a conductive knitted fabric. While U.S. Pat. Nos. 4,443,515, issued to Atlas, and its divisional 4,484,926, disclose that conductive fibers comprised of synthetic polymers may be incorporated into knitted fabrics, those references do not disclose a pattern whereby such conductive fibers can be economically incorporated into a knitted fabric so as to dissipate static electricity in any direction along the course and wale directions of the fabric.
U.S. Pat. No. 4,398,277, issued to Christiansen et al., does disclose a pattern whereby insulative yarn and electrically conductive yarn are knitted together on two levels The insulative yarn in Christiansen et al. forms a series of interlocking loops on both the technical face and back of the fabric in a tricot construction, while the electrically conductive yarn forms a series of chain stitches on only the technical face. Christiansen et al. disclose that when their fabric is knitted in such a two layer construction, one of the surfaces (i.e., the technical face) will be relatively nonconductive. Electrical charge dissipation in such a construction, therefore, is limited to the wale direction of the technical face of the fabric.
Attempts have been made to develop a knitware pattern that can be economically manufactured, which require the use of a relatively small amount of conductive fiber and which possess electrical conductivity along both the course and wale directions and on both the technical face and back of a two layer knitted fabric. A knitted fabric in which conductive yarn is knitted in an argyle pattern together with nonconductive yarn, resulting in a fabric having electrical conductivity along the course and wale directions on both the technical face and back, has been constructed.
The argyle construction suffers from several disadvantages. Such a construction requires that the conductive fiber be stitched simultaneously along both the course and wale directions to form a saw-tooth pattern known as an "Atlas stitch" which, when joined to a similar adjacent stitch, forms the argyle pattern. Such simultaneous horizontal and vertical movement of fiber requires that the argyle knit be manufactured on a knitting machine having at least two separate guidebars dedicated to the argyle construction. Further, the argyle construction requires the use of a substantial amount of conductive yarn, which is a significant disadvantage given that such yarn is currently more than about thirty-six times as expensive as nonconductive yarn. An additional significant disadvantage of this conductive argyle construction is that it can only be fabricated by a relatively complex warp knitting machine, i.e., one having two or more dedicated guidebars as mentioned above.
A need exists, therefore, for a relatively inexpensive easily knitted fabric capable of rapidly and effectively discharging static electricity. Further, the need exists for such a knitted fabric which is capable of discharging static electricity along the course and the wale directions of the fabric and on the technical back and/or face of the fabric. Further, there is also a need for such an antistatic knitted fabric which can be manufactured on a conventional knitting machine that is not as mechanically complex as those required for complex knits, e.g., double argyle, presently used in the industry.
Accordingly it is an object of the present invention to provide a knitted fabric having improved electrical charge dissipation properties.
It is a further object of the present invention to provide such a knitted fabric in which an electrostatic charge can be dissipated both along the course direction of the knitted fabric and the wale direction of the knitted fabric on the technical back and/or face.
It is a further object of the present invention to provide a knitted fabric having improved electrical discharge dissipation properties in which the percentage of conductive fiber employed in the fabric is significantly less than that required in knitware construction disclosed in the prior art.
It is a still further object of the present invention to provide a knitted fabric which can be manufactured on a conventional knitting machine that is mechanically less complex than those machines presently used to manufacture conductive knitware, i.e., one that requires the use of only one dedicated guidebar.
Other objects and advantages will be in part obvious and in part hereinafter pointed out.